For the past forty years anechoic chambers and ground plane ranges have been used to measure radar scattering from targets in order to measure the radar cross-section of such targets. The ground plane range has been successfully employed to measure large targets at close-to-far field conditions. In the ground plane range, a transmitter/receiver antenna is used to beam an electromagnetic wave at a target supported by a pylon and to measure the backscattered radiation to determine the radar cross-section.
The ground plane range utilizes the earth as a reflecting plane to increase antenna gain in the vicinity of the target. This provides an overall 12db signal to noise improvement for isotropic antennas over a perfect reflecting plane. This feature while improving gain restricts the region of uniform amplitude in the vertical plane due to the interaction of the phase of the direct ray-wave path and the reflected ray-wave path. The region of uniform amplitude increases as the target is raised and the antenna is lowered and decreases as the target is lowered and the antenna is raised. The latter situation is often preferred, however, since raising the antenna allows the antenna to be raised above the ground plane (below which a portion of the antenna has often had to be recessed in a pit), and the use of a larger antenna to provide more power on the target.
In the latter situation, however, the target has to be lowered thereby allowing radiation which has scattered to the ground plane and reflected back to the target to be backscattered from the target to the receiving antenna causing a false signal reading. This radiation is often referred to as two-way ground clutter while radiation that has scattered to the ground plane and reflected to the antenna is often referred to as one-way ground clutter. While this backscattered radiation can be gated out if the target is raised sufficiently above the ground plane, such an increase in height would necessitate the transmitting antenna to be lowered, thus made smaller and recessed into the ground plane, would broaden and lose power on the transmitting beam, and would cause additional unwanted backscatter from the higher and larger pylon structure needed to raise the target further above the ground plane.
Accordingly, it is a general object of the present invention to provide an improved radar range.
It is another object of the present invention to provide a radar range which permits the use of larger and higher transmitting antennas.
It is a further object of the present invention to provide a radar range which has decreased backscatter from the supporting structure for a radar target.
It is still another object of the present invention to provide a radar range which permits a sharper and more powerful radar beam to be directed on a target.
It is still another object of the present invention to provide a radar range in which the target can be lowered without introducing spurious backscattered radiation due to one-way and two-way ground clutter.
The novel features which are believed to be characteristic of the invention, both as to its organization and its method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.